Design a Todo List Object Model

Design the object-oriented model for a todo list application. The product should allow a user to create multiple todo lists or projects, create tasks, update task fields, mark tasks complete or incomplete, delete tasks, set due dates, assign priorities, add tags, and filter or sort tasks by status, due date, priority, and tag. Describe the main classes, their responsibilities, the public APIs you would expose, and how you would keep the design extensible for features such as reminders, recurring tasks, and collaboration.